Synonyms of insidious

insidious

adjective

as in treacherous

formal causing harm in a way that is gradual or not easily noticed

Most people with this insidious disease have no idea that they are infected.

an insidious enemy

Related Words

• treacherous
• subtle
• perfidious
• deceptive
• false
• misleading
• deceitful
• incorrect
• cunning
• wrong
• specious
• wily
• beguiling
• sneaky
• delusive
• fallacious
• devious
• trick
• underhanded
• crafty
• tricky
• sly
• perplexing
• artful
• subtile
• deceiving
• delusory
• fast
• shady
• underhand
• ambiguous
• confounding
• shifty
• inaccurate
• puzzling
• fraudulent
• slick
• foxy
• distracting
• mendacious
• guileful
• duplicitous
• deluding
• untrustworthy
• sneaking
• trickish
• bewildering
• lying
• untruthful
• dishonest
• artificial
• evasive
• faithless
• spurious
• bogus
• counterfeit
• hypocritical
• crooked
• knavish
• phony
• circuitous
• sham
• feigned
• ambidextrous
• fake
• dissembling
• forged
• equivocal
• insincere
• double-dealing
• jive
• backhanded
• defrauding
• two-faced
• left-handed

Dissimilar Words

• direct
• plain
• outspoken
• frank
• open
• candid
• illuminating
• straight
• explanatory
• revealing
• revelatory
• clarifying
• free-spoken
• truthful
• openhearted
• plainspoken
• honest
• elucidative
• trustworthy
• foursquare
• straightforward
• forthright
• aboveboard
• nondeceptive

Example Sentences

Recent Examples of insidious

But there’s a market for a darker and more insidious explanation as to how the world works. — James Kirchick, The Atlantic, 29 July 2026

Meanwhile, an insidious supervillain (Kenneth Branagh) lurks, threatening to take Crown down. — Mya Copeland, Variety, 29 July 2026

But there’s a historical, and some might argue insidious, irony to all of this. — Drew Pittock, USA Today, 25 July 2026

But, as Ellis demonstrates in this survey of the city’s racial history, liberal policy achievements tend to obscure more insidious forms of exclusion. — The New Yorker, New Yorker, 20 July 2026